This invention relates to an apparatus for control of an oil-pressure-operated transmission used for a vehicle such as a motorcar or the like.
As for the apparatus of this kind, there has been known a type of apparatus with a transmission provided with at least two-speeds forward driving trains having respective oil pressure clutches interposed therein, a backward driving train in which one of the oil pressure clutches used in the forward driving trains is used also for decreasing the size of the apparatus, and a selector arranged to be given changeover movements between its forward running side and its reverse running side for selectively establishing either the one of the forward driving trains or the reverse driving train, and a manual valve is interposed in an operation circuit of the transmission so that when the manual valve is in its automatic shift range on its forward running side, the selector is given a changeover movement to its forward running side and the respective oil pressure clutches in the forward driving trains are receiving the pressure oil from an oil pressure source through a shift valve, whereby there is effected a forward running of the vehicle at a predetermined gear by one or the other of the two forward driving trains according to a changeover movement of the shift valve corresponding to a vehicle speed and a throttle open degree, and when the manual valve is in its backward running range, the selector is given a changeover movement to its backward running side and the oil pressure clutch for common use is receiving pressure oil, causing a backward running of the vehicle by the reverse driving train. With this conventional apparatus, it has been usual, that the supply of the pressure oil to the oil pressure clutch for common use in the backward running range may be effected through the shift valve as shown, for instance, in FIG. 1. This conventional arrangement, however, has a connected defect that if the shift valve a is locked due to dust contamination or the like at such a position, for instance, that a pressure oil supply passage b, in the automatic shift range, is in connection with any of oil passages c' and d' respectively connected to the oil pressure clutch for common use c and the other oil pressure clutch d, it is possible to connect a pressure oil supply passage e, in the backward running range, with the oil passage c' connected to the common use oil pressure clutch c, and consequently there cannot be achieved a reverse running of the vehicle.